A terror attack on supporters watching Euro 2016 has been foiled with just hours to spare, Belgian officials indicated yesterday, as 12 suspected jihadists were arrested in a major security alert.

Officers rounded up 40 people of interest during swoops linked to an alleged plot to attack fans in Brussels gathering to watch Belgium's match against Ireland on Saturday afternoon.

The raids come after authorities warned of a squad of armed Isil commandos preparing "imminent" strikes in France and Belgium.

A jihadist cell was said to have left Syria a week ago to commit an atrocity in both countries, according to an earlier intelligence leak.

Belgium police have so far refused to clarify whether the overnight raids were linked to earlier warnings.

Prime Minister Charles Michel held an urgent meeting with the government's security council - which includes the ministers of defence, justice, home affairs and foreign affairs.

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The terrorist cell was plotting an attack in Brussels later on Saturday, public broadcaster VTM reported, and the suspects were seen driving near a fanzone in Brussels, according to reports.

The Belgian federal prosecutor's office said no weapons or explosives had been found during the overnight searches, which also involved 152 garage lockups.

"In connection with a criminal investigation concerning terrorism ... 40 persons were taken for questioning," the Belgian federal prosecutor's office said. "Twelve among them were arrested.

"The investigating judge will decide on their possible detention later today. The investigatory results necessitated an immediate intervention. The investigation continues." Belgian newspaper Le Soir said areas where fans watch matches were potential targets, as well as other crowded areas such as shopping centres and stations, citing a security source.

The "Foot Euro 2016 Village Rogier" fanzone in Brussels was one of the potential sites targeted in the thwarted attacks, Belgium's De Standaard newspaper said.

Security measures there have been increased, it said, with body searches implemented and a total ban on people bringing in bags or backpacks.

Dernière Heure newspaper, which said it had obtained an alert message, reported fighters travelling without passports were believed to be trying to reach Europe by boat via Turkey and Greece.

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"These people are thought to have split into two groups - one for Belgium, the other for France in order to commit terror attacks in groups of two," it was cited as warning.

While Dernière Heure makes no mention of specific threats to football stadiums or other targets in France, it cites more precise information on three Belgian targets.

These include "a big Brussels shopping centre, a restaurant of a American fast food chain (not localised) and a police target, such as a police station (not localised)".

France, however, "remains the preferred target for Isil," wrote DH, citing Belgian intelligence.

It was also reported Mohamed Abrini, the terror suspect arrested in the wake of the attacks on Brussels airport and metro in March that killed 32, has managed to communicate with the outside world despite being confined to a prison in Beveren.

A message scrawled in Arabic on an A4 piece of paper that was intercepted by a fellow inmate and handed to prison authorities reads: "Something is moving in France".

Belgium's crisis centre is said to have placed several government ministers, including the prime minister, under heightened protection on Friday.

Security around all the teams involved in Euro 2016 has been heightened in recent months but French authorities are at full stretch as they deal with the twin threats of hooliganism and terrorism.